mammograms

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Any procedure that involves sandwiching your naked breast between hard glass plates is personal. Very. But it’s becoming ever more clear that getting a mammogram also holds an element of personal decision. Medical authorities put out broad guidelines, but then you and your doctor can customize them, based in part on your own breast cancer risk and preferences.

How? Before we get into that, a paper just out in the Journal of the American Medical Association takes a sweeping look at a half century of mammogram data, and offers this big picture: mammograms do save lives, “but those benefits are not enormous,” said Dr. Nancy Keating of Brigham and Women’s Hospital and Harvard Medical School, the paper’s co-author. While the potential harms — that a woman will undergo cancer treatment for a tumor that never would have actually harmed her — have tended to be underestimated.

Here, Dr. Keating lays out the mammogram numbers that I found most helpful:

“If we take 10,000 women who are at average risk at age 40, over the course of ten years about 190 will be diagnosed with breast cancer. Most of these women will do well and would have done well regardless of screening. About five of those 10,000 women will have their life saved by the mammogram. Another 30 of those women will die regardless of the mammogram because unforutunately some breast cancers are so aggressive that they’re destined to be deadly despite the mammogram.

So there is benefit, five out of 10,000 women have their lives saved, but there are also these harms. One harm is false positives and unnecessary biopsies,: Of 10,000 women, about 6,000 will have at least one false positive. At this point, I say to patients, ‘You should expect that you’ll have some false positives, and don’t worry when they call you back.’ The over-diagnosis harm, we estimate: about 36 of those 190 cancers that were diagnosed could be over-diagnosed, and so those women will be treated — because we can’t currently tell the difference between the cancers we need to worry about and those that might not be so concerning, so we treat them all the same. So those women are then subjected to the harms of treatment without gaining any benefits.

It’s just hard to wrap your head around. Cancer screening tests — mammograms, PSA levels, colonoscopies — check for early tumors. Catching cancer earlier is better than later. And yet some research suggests that screening — at least for breast and prostate cancer — may be of dubious worth, because it catches many cancers that would never have posed a danger.

…More than a million women who were told they had early stage cancer — most of whom underwent surgery, chemotherapy or radiation — for a “cancer” that was never going to make them sick. Although it’s impossible to know which women these are, that’s some pretty serious harm.

But even more damaging is what these data suggest about the benefit of screening. If it does not advance the time of diagnosis of late-stage cancer, it won’t reduce mortality. In fact, we found no change in the number of women with life-threatening metastatic breast cancer.

Have lingering questions? Tune in to Radio Boston today a little after 3 p.m. for a discussion of the issue that will include a chance to call in. And it may help to view the video above, in which Dr. Welch explains his findings.

We already knew this about guns and knives hidden in baggage. Now it seems the same important insight applies to cancers hidden in breasts: When the target of a visual search — like a weapon or a tumor — occurs only rarely, we’re far likelier to miss it than if it were much more common.

Jeremy Wolfe, director of the Visual Attention Lab at Brigham and Women’s Hospital, uses this pithy phrase for the problem: “If you don’t find it often, you often don’t find it.”

And a problem it is, from airport security to pap smears. Growing research suggests that because some of the perils we most want to seek and destroy are extremely rare, we’re naturally ill-suited to the task.

A cognitive scientist and vision expert, Wolfe began applying his lab’s work to airport security in the years after 9/11. Now he has just presented real-world findings on breast cancer at the annual convention of the Radiological Society of North America, a gathering of tens of thousands of medical scanning professionals.

Typically, mammography turns up three or four cases of breast cancer for every 1,000 scans, but misses 20-30% of tumors, Wolfe said. His central finding: As many as half of those misses could be the result of the “behavioral effects of searching for something very rare.”

First, to clarify the point, using an example from Wolfe’s convention talk based on lab experiments:

Imagine you have X-rays of 20 bags with guns and knives in them. Mix them into a stack of 40 X-rays in total, so the “prevalence” of weapons is 50%, one in two. If you were a typical scan-checker in Wolfe’s experiment, you would fail to catch only four or so of those 20 hidden weapons.

Now imagine those same weapon-laden 20 suitcases are mixed in a pile of 1,000 bags, so the prevalence of weapons is a mere 2%. It’s the same 20 bags, but your “miss” rate more than doubles, from missing perhaps four weapons to perhaps eight or nine.

Why? These searches are hard tasks, exhausting for our fallible human eyes and brains. Plus, we have a built-in hesitancy about saying we have found something rare. And when targets are rare, we tend to give up more quickly.

Go look for a zebra

Say I tell you to go out to the streets of Boston and look for a zebra, Wolfe said. Continue reading →

Are you more comfortable knowing you’ve done everything you can to prevent breast cancer? Or are you annoyed by the pushiness of screening advocates, and convinced by data suggesting that it’s often over-diagnosed and over-treated?

A study published last week in the British Medical Journal added another twist to the longstanding debate, by suggesting that better treatments – not mammography – deserve credit for the drop in breast cancer deaths since the mid-1990s.

The study looked at pairs of northern European countries or regions; one that introduced universal screening many years before the other. Sweden, for instance, began universal screening in 1986, a dozen years before neighboring Norway. Researchers found breast cancer death rates were virtually identical on either side of the border, suggesting, they said, “that screening has not played a direct part in the reductions of breast cancer mortality.”

If this is true, we should be putting more emphasis on treatment advances, and far less on getting every woman over a certain age to get a mammogram.

That’s precisely what Dr. H. Gilbert Welch, professor of medicine at the Dartmouth Institute for Health Policy and Clinical Practice, thinks should happen.

There’s no question that mammography saves lives, Welch says, but it’s not as good a screen as most people think. About 2,500 women over 50 have to be screened every year for 10 years to save one life, he wrote in a New England Journal of Medicineeditorial last year. Up to 1,000 of those women will have at least one false positive, and 5 to 15 of them will be treated needlessly for breast cancer they don’t have.

“We’ve exaggerated its effect grossly. And we haven’t acknowledged – in fact we’ve largely ignored – its harm,” Welch said. (Welch qualified his statement in a follow-up email: his complaint is with using mammography to screen a broad swath of people, most of whom have no symptoms. It is an appropriate test, he said, when used to examine women with suspicious lumps or other symptoms.) Continue reading →

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Massachusetts is the leading laboratory for health care reform in the nation, and a hub of medical innovation. From the lab to your doctor’s office, from the broad political stage to the numbers on your scale, we’d like CommonHealth to be your go-to source for news, conversation and smart analysis. Your hosts are Carey Goldberg, former Boston bureau chief of The New York Times, and Rachel Zimmerman, former health and medicine reporter for The Wall Street Journal.

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